It is possible as a result of a defect for gas to be produced in lithium ion battery cells. As a consequence, an excess pressure arises inside the lithium ion battery cells. In the presence of a defined pressure inside a battery cell of this type, an excess pressure valve opens in order to discharge the gases and to avoid the battery cell becoming thermally unstable. During this process, graphite dust that is released from the graphite cathode of a battery cell of this type is also discharged and deposits itself on the surface of the battery cell.
It is known from the prior art to use capacitance sensors for many purposes such as by way of example for ascertaining spacings, pressures, fill levels or moisture contents. Capacitance sensors function on the basis of the change in the capacitance of an individual capacitor or of an entire capacitor system. The capacitance can be influenced in numerous ways that mostly arise as a result of the selected application.